The invention relates to a sewing machine, and more particularly relates to a free arm sewing machine. A sewing machine body is connected to a base by a pivot structure, and a positioning device is provided to change the sewing machine into a flat bed working condition and into a free arm working condition. The invention also relates to a free arm sewing machine which is modified to provide a lower machine bed, on which the sewing work is performed, especially when the sewing machine is used as a flat bed sewing machine when is so frequently employed. In fact, the machine bed of the sewing machine is lowered in such a degree that the underside at the end of the free arm contacts the upper face of a table on which the sewing machine is placed, for the purpose of providing an efficient sewing work to the machine operator.
Generally a free arm sewing machine, which may be used as a flat bed sewing machine by employing an auxiliary bed plate, has a free arm 1 which is spaced (clearance C) from the lower machine base 2 as shown in FIG. 1, so that a fabric to be sewn may be inserted over the free arm. This type of the sewing machine requires at least the height H.sub.1 from the upper face of the table S to the sewing work face 3a of the sewing machine as shown in FIGS. 1 and 2. The reference numeral 3 denotes an auxiliary bed plate which is employed when the sewing machine is used as a flat bed sewing machine. The auxiliary bed plate 3 is removed when the sewing machine is used as a free arm sewing machine, and may be used as a case for accommodating the accessories of the sewing machine. In case a sewing operation is performed by a sewing machine placed on a table, it can be said that a more efficient and smoother sewing operation is possible if the physical working level of the sewing machine is lowered. The tables generally available on the market are so designed and standardized as to be most suitable for working thereon. It is, therefore, apparent that the sewing work efficiency is so lessened if the sewing machine with the working level H is placed on the table. The most suitable height or level of the table is such that the elbows of the operator lightly touch the upper face S of the table.
FIG. 2 shows a stitching operation with a sewing machine as shown in FIG. 1 which is placed on the table S as abovementioned. In this case, since the working level of the sewing machine is H.sub.1, the machine operator must raise the hands to the level H.sub.1 from the elbow.
FIG. 3 shows a sewing machine in which the base 4 is lowered partly on the side of the free arm 5. In this case, the working level H.sub.2 is lower than that of the sewing machine in FIG. 1. Instead, the sewing machine in FIG. 3 is structurally unstable. It becomes, therefore, necessary to provide an auxiliary foot 6 as shown. By the way, the reference numeral 7 denotes an auxiliary table plate of the same function as that 3 in FIG. 1.
As well known, the free arm sewing machine requires at least the vertical thickness of the free arm and an additional clearance between the free arm and the upper face of the table for inserting a sewn fabric over the free arm. The sewing machine of the type, however, is normally used as a flat bed sewing machine, and is not so often as a free arm sewing machine. It is, therefore, important to design the working level of the sewing machine on the side of the flat bed sewing machine.